1. Field of the Invention
This disclosure relates to fluid control devices and in particular relates to devices used to control flow between a fluid input and a fluid output.
2. Description of the Related Art
Fluid flow systems where fluid flow rate needs to be precisely controlled are required in many health and industrial applications. For example, a fluid flow system may be used in a ventilator system used to administer oxygen mixed with air for a controllable breathing mixture for patients requiring breathing assistance. It is vital that a correct oxygen/air mixture is used to prevent oxygen toxicity. It is well known that elevated partial pressures of oxygen may result in cell damage and death.
Generally needle valve assemblies have been used to precisely control the fluid flow between a fluid input and a fluid output. Needle valves are costly and difficult to manufacture due to stringent machining requirements and the high degree of precision required. A needle valve is required to control the fluid flow at each valve station. Each valve station must be wider than would otherwise be required in order to accommodate the needle valve hardware. The needle valve is mounted directly to the manifold. In order to mount the needle valve assembly, the manifold needs to be precisely machined and assembled. The needle must fit concentric to the opening in the manifold and must enter the inlet flow path at right angles. If the needle is threaded in too far it will bend or break, often the operator is unaware of the damage. Additionally it is nearly impossible to completely shut off the flow because of a round needle entering a round flow path at right angles.